Defibrillator systems provide measured amounts of electrical energy for shocking a cardiac patient. A defibrillator system also typically includes ECG monitoring apparatus. ECG data acquired by the monitoring apparatus may be displayed for example on a CRT built into the defibrillator unit and/or recorded on hard copy or other data storage means. The ECG front end which is used to acquire ECG data also may be used for triggering the defibrillator for synchronized cardioversion. The ECG front end can acquire ECG data from the patient either through external paddles, which also are used to administer a shock to the patient, or through a separate set of leads coupled to ECG electrodes.
Various pads or paddles may be connected, one at a time, to the defibrillator base unit for conveying electrical energy to the patient. However, it is essential for the defibrillator base unit to identify what type of pads or paddles are presently connected to it, as well as to detect when no pads or paddles are connected to the unit. The selected pads or paddles may be identified by the user, and the selection input to the base unit by setting a switch or pressing a button. This method, however, is subject to user error, and adds complexity to the user interface or keypanel. Moreover, this step adds to the setup time in an application where a patient's life may be in danger and, therefore, time is of the essence. It would be preferable to automatically identify the connected pads or paddles to the defibrillator base unit without operator input.
One way to automatically identify the selected paddle assembly is a binary encoding scheme in which two or more signal lines are used as bits to encode an identifying number. Two bits of data thus could be used to identify one of four types of pads or paddles, and three bits of data would identify one out of eight. Each pad or paddle assembly could include an identification circuit arranged to assert the various signal lines to logic hi or low levels according to the encoding scheme. A supply voltage and ground lines thus would also be required. However, it is desirable to minimize the number of such signal lines and thus keep the interface between the base unit and the various paddle assemblies as simple as possible.
Moreover, it is difficult if not impossible to provide electronic identification circuits in some types of paddles. For example, internal paddle assemblies (those that are used inside a patient's body during surgery) must be sterilizable. Any electronic circuitry required within the internal paddles assembly would have to be encapsulated in a sterilizable package at considerable cost and complexity of manufacture. In the case of adhesive pads, the pads are discarded rather than sterilized and reused, so their cost also is of particular concern. Accordingly, electronic circuitry for identifying the pads must be kept to a minimum or avoided entirely, if possible.
Accordingly, the need remains for a defibrillator patient connection system that automatically identifies a type of pads or paddles connected to a defibrillator base unit, while maintaining a simple interface between the base unit and the paddle assemblies, and keeping electronic circuitry to a minimum in certain types of paddles.